The present invention relates to a alkenyl aromatic resin composition having an excellent impact strength. More particularly, it relates to a alkenyl aromatic resin composition prepared by blending a random segmented copolymer with a rubber-modified alkenyl aromatic resin or a resinous mixture containing the resin thereof.
Rubber-modified alkenyl aromatic resins containing from 2 to 35 wt. % of conjugated diolefin components or resinous mixtures containing at least one of these components, which are exemplified by rubber-modified polystyrene, acrylonitrile-butadiene-styrene copolymer, methylmethacrylate-butadiene-styrene copolymer, and polyphenylene ether resin containing rubber-modified polystyrene, have so far been commercially available.
These rubber-modified alkenyl aromatic resins have been used as various products such as packaging materials, electrical parts, automobile parts, and architectural decorations, taking full advantage of their rigidity, high impact strength and processability.
Conventionally, manufacturers had selected one or more of these commercially available rubber-modified alkenyl aromatic resins, while taking account of costs and physical properties, and had used them alone or in the form of blends, to manufacture those products which could meet the demands from end users. However, there have been frequent occasions in which commercially available rubber-modified alkenyl aromatic resins had such insufficient impact strength that manufacturers often could not produce those high-impact resistant products which might satisfy their end users. Therefore, there has been great expectations for the development of blending technology that can improve the impact strength of commercially available rubber-modified alkenyl aromatic resins without adversely affecting other physical properties.
As one of the methods of improving impact strength of rubber-modified alkenyl aromatic resins, it has already been known to use a block copolymer of a vinyl-substituted aromatic compound and a conjugated diolefin as a toughening agent for alkenyl aromatic resins. British Pat. No. 1,077,769 and Japanese Preliminary Publication of Patent No. 56250/1973, for example, describe the use of a block copolymer of the ideal type which consists of a vinyl-substituted aromatic polymer block and a conjugated diolefin polymer block. Japanese Preliminary Publication of Patent No. 108455/1977 describes a radial teleblock copolymer of the ideal type to be used as a toughening agent for a polyphenylene ether resin composition consisting of a polyphenylene ether resin and a rubber-modified polystyrene.
However, these resin compositions consisting of a block copolymer and a rubber-modified alkenyl aromatic resin, described in the above references, do not exhibit full effect in improving the impact strength unless the compositions contain a relatively large amount of the block copolymer. Unfortunately, the addition of a large amount of block copolymer to a rubber-modified alkenyl aromatic resin composition brings about a practically unfavorable result, because mechanical properties such as rigidity and tensile strength will decrease.
In view of the present circumstances, the inventors have studied intensely to develop a highly efficient toughening agent used for a rubber-modified alkenyl aromatic resin or a resinous mixture containing the resin thereof. It has been discovered from these studies that, when a specific random segmented copolymer is added to a rubber-modified alkenyl aromatic resin or a resinous mixture containing the resin thereof, the obtained resin composition exhibits greatly improved impact strength, without adversely affecting any other mechanical properties. Such a discovery has led the inventors to complete the present invention.